During the manufacture, conveyance, and storage of calcium hydroxide, Ca(OH).sub.2, sometimes referred to as hydrated lime, the presence of CO.sub.2 in the air which comes in contact with the hydrated lime can compromise the chemical integrity of the hydrated lime. While hydrated lime has a greater moisture stability than calcium oxide, hydrated lime is perishable unless adequately protected from CO.sub.2 absorption. Hydrated lime has a strong affinity for CO.sub.2 even in dilute concentrations. When hydrated lime absorbs CO.sub.2 from the air, an undesirable reaction known as recarbonation occurs and the Ca(OH).sub.2 is converted to calcium carbonate, CaCO.sub.3. It is known that CaCO.sub.3 can deposit as scale on the walls of conduits in pneumatic conveying systems. As these deposits build up, they can sometimes totally occlude the conduit.
Hydrated lime in storage containers can absorb CO.sub.2 from the air in the storage container. Also, as hydrated lime is milled into smaller particles during manufacturing, the hydrated lime becomes more susceptible to CO.sub.2 absorption. This is because as the lime is milled into smaller particles, the surface area per unit volume of lime increases. The increased surface area per unit volume will increase the CO.sub.2 absorption rate of the lime making it susceptible to chemical degradation.
The chemical integrity of hydrated lime can be protected using an inert gas such as nitrogen for blanketing storage containers, milling machines, and conveying systems. However, commercial generators of nitrogen are expensive to install and maintain.
It would be desirable to provide inexpensive, easy to maintain apparatus and methods that provide air with a reduced CO.sub.2 content. The reduced CO.sub.2 content air could then be used in manufacturing, conveying and storing hydrated lime such that the chemical integrity of the hydrated lime is not degraded.